During the steel making processes, a large amount of steel-making slag is generated. Although the steel-making slag contains, for example, P and metal components such as Fe and Mn, it also contains a large amount of CaO, which leads to expansion and collapse. This has restricted the steel-making slag to be used as, for example, a material for roadbed or aggregate. However, in recent years, resources have been increasingly recycled, and a large number of methods for recovering the valuable substances from the steel-making slag has been disclosed.
Patent Document 1 discloses a method of processing iron and steel slag, which includes adding iron and steel slag generated during melting and making iron and steel, to molten iron and steel liquid in a smelting furnace, further adding heat and reducing agents, moving Fe, Mn, and P to the molten liquid while altering the iron and steel slag to obtain altered slag, and then, moving Mn and P in the molten liquid into the slag. However, this processing method requires batch processing to be continuously applied several times until the slag with predetermined components can be obtained, and hence, results in poor working efficiency.
Non-Patent Document 1 discloses results of reduction tests in which steel-making slag powder, carbon material powder, and slag-modifying agent powder are inserted through a hollow electrode into an electric furnace. However, in the reduction tests described in Non-Patent Document 1, processing is performed in the electric furnace to the cold steel-making slag that has been solidified and crushed, which leads to an increase in the energy-consumption rate.
Further, Patent Document 2 discloses a technique of recovering valuable metals by reducing molten slags generated during smelting of non-ferrous metals using carbonaceous reducing agents in an open-type direct-current electric furnace to separate it into a metal phase and a slag phase. However, the method described in Patent Document 2 also involves batch processing in the electric furnace with the target of processing being the cold slag, which also leads to an increase in the energy-consumption rate.
As described above, these conventional methods of recovering valuable components from the slags each have a problem of poor working efficiency or large energy-consumption rate.